The measurement of differential pressure is important in many applications such as those measuring oil pressures, fuel pressure, hydraulic pressure, air pressure, and the like. In many of these applications, it may not be desirable to measure differential pressure by applying different pressures to opposite sides of a sensor's diaphragm. Instead, a half-bridge sensor configuration may be used, such as described in U.S. Pat. No. 4,695,817, entitled “ENVIRONMENTALLY PROTECTED PRESSURE TRANSDUCERS EMPLOYING TWO ELECTRICALLY INTERCONNECTED TRANSDUCER ARRAYS,” issued Sep. 22, 1987 to Dr. Anthony D. Kurtz et al, and assigned to Kulite Semiconductor Products, Inc., the assignee herein. This configuration has many benefits but may be susceptible to thermal gradients, since each side of the differential sensor may be physically located in different environments. In some applications, a hot liquid such as engine oil may be applied to the front half-bridge of the sensor's diaphragm, while a cool gas such as atmospheric air may be applied to the back half bridge of the sensor's diaphragm. In this case, compensating for the temperature difference between each of the sensor's diaphragm may be difficult. Typical temperature compensation of half-bridge sensors assume that both sensors are at the same temperature, so that any temperature effects may be compensated using temperature compensation techniques such as described in U.S. Pat. No. 3,245,252, entitled “TEMPERATURE COMPENSATED SEMICONDUCTOR STRAIN GAGE UNIT” issued Apr. 12, 1966 to Dr. Anthony Kurtz et al., and assigned to Kulite Semiconductor Products, Inc., the assignee herein.
FIG. 1 shows a prior art sensor 100 having thermal gradients. In FIG. 1, the sensor 100 includes a main half-bridge transducer 101, a reference half-bridge transducer 105, a single span resistor 108, a shunt resistor 109, input terminals 121 and 122 and output terminals 123 and 124. The main half-bridge transducer 101 includes piezoresistive elements 102 and 103. Similarly, the reference half-bridge transducer 105 includes piezoresistive elements 106 and 107. Each of the piezoresistive elements 102, 103, 106 and 107 may also be referred to as a leg of a Wheatstone bridge. Further, each set of the piezoresistive elements 102 and 103 and the piezoresistive elements 106 and 107 may be referred to as a piezoresistive gauge. The main half-bridge transducer 101 and the reference half-bridge transducer 105 are coupled to the single span resistor 108, which acts as a voltage divider. As a temperature of each of the main half-bridge transducer 101 and the reference half-bridge transducer 105 increases, a resistance of a piezoresistive gage of each of the main half-bridge transducer 101 and the reference half-bridge transducer 105 increases, resulting in an increase in a voltage applied to each of the main half-bridge transducer 101 and the reference half-bridge transducer 105. Thus, the use of the single span resistor 108 in this configuration compensates for a decrease in sensitivity with increasing temperature.
In FIG. 1, the shunt resistor 109 is coupled across the piezoresistive element 102 of the main half-bridge transducer 101. The shunt resistor 109 compensates for a thermal zero shift associated with the sensor 100 by shunting more current from the piezoresistive element 102 as the temperature increases and a resistance of the piezoresistive element 102 increases. This technique works well when the piezoresistive elements 102 and 103 of the main half-bridge transducer 101 and the piezoresistive elements 106 and 107 of the reference half-bridge transducer 105 are at an equivalent temperature. However, when the main half-bridge transducer 101 and the reference half-bridge transducer 105 are not at an equivalent temperature, then one of the transducers 101 and 105 will have increased resistance due to the temperature difference. The use of the shunt resistor 109 in this configuration still adjusts for a thermal zero shift between the main half-bridge transducer 101 and the reference half-bridge transducer 105, resulting in the sensor 100 having measurement errors over temperature. Accordingly, there is a need for improved techniques to allow for compensating sensors having thermal gradients. In addition, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and claims, taken in conjunction with the accompanying figures and the foregoing technical field and background.